Fixes #5371 Make Piwik work PHP session hash function is non default …

…such as sha1 or sha512 or other

id is now VARCHAR field

Tested with: session.hash_function = sha256

Had to use VARCHAR as the session id can be 128 chars eg.
```
$ php -r "var_dump(hash('sha512','test'));"
string(128) "ee26b0dd4af7e749aa1a8ee3c10ae9923f618980772e473f8819a5d4940e0db27ac185f8a0e1d5f84f88bc887fd67b143732c304cc5fa9ad8e6f57f50028a8ff"
```

core/Db/Schema/Mysql.php

@@ -299,7 +299,7 @@ public function getTablesCreateSql()
 			",
 
             'session'               => "CREATE TABLE {$prefixTables}session (
-								id CHAR(32) NOT NULL,
+								id VARCHAR( 255 ) NOT NULL,
 								modified INTEGER,
 								lifetime INTEGER,
 								data TEXT,

core/Updates/2.4.0-b8.php

@@ -0,0 +1,29 @@
+<?php
+/**
+ * Piwik - free/libre analytics platform
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ */
+namespace Piwik\Updates;
+
+use Piwik\Common;
+use Piwik\Updater;
+use Piwik\Updates;
+
+class Updates_2_4_0_b8 extends Updates
+{
+    static function getSql()
+    {
+        return array(
+            "ALTER TABLE `" . Common::prefixTable('session')
+            . "` CHANGE `id` `id` VARCHAR( 255 ) NOT NULL " => false,
+        );
+    }
+
+    static function update()
+    {
+        Updater::updateDatabase(__FILE__, self::getSql());
+    }
+}

core/Version.php

@@ -21,5 +21,5 @@ final class Version
      * The current Piwik version.
      * @var string
      */
-    const VERSION = '2.4.0-b7';
+    const VERSION = '2.4.0-b8';
 }